1. Field of the Invention
Utilization of metal chips, especially scrap metal chips, particularly brass, aluminum, magnesium, titanium, and alloys thereof, by introduction of said metal chips into a mass of molten metal of which they are formed or an alloy thereof and at or below the surface thereof.
Minimizing fuel cost, heat loss, and conversion of the metal at the surface of the molten mass to metal oxide, as well as increasing the yield of utilizable metal from such remelting or recycling operation to nearly the theoretical, by maintaining a non-oxidizing atmosphere or environment at the surface of the molten metal mass and, optionally and advantageously, utilizing vaporizable residual impurities on chips being recycled such as oil, lacquer, or like vaporizable impurity to assist in maintaining the non-oxidizing atmosphere or environment, thereby optionally and advantageously permitting the elimination of previously-employed impurity-removal steps in preparation of the chips for industrial utilization or recycling by introduction into the said molten metal mass; conveniently and simultaneously eliminating environmental contamination from vaporizable impurities, fumes, and decomposition products thereof. Apparatus suitable for use in the process.
2. Prior Art
The state of the art has been fully reviewed in the prior U.S. patents of one of us, namely, U.S. Pat. Nos. 4,702,768, 4,710,126, 4,721,457, and 4,872,907, the disclosures of which patents are incorporated herein by reference. Although much progress has been made in the field of conversion of metal chips, and especially recycled metal chips, into utilizable industrial metal by the remelting thereof, as indicated by these patents and their solutions to some of the most significant problems involved, serious economic and environmental shortcomings still remain in the overall procedure, which act as both industrial and economic impediments to the fullest utilization and reutilization of metal chips and their conversion into industrially-utilizable "new" metal.
Some of the most important drawbacks involve excessive fuel cost because of heat losses from the furnace in which the mass of molten metal is contained and loss of excessive amounts of metal by conversion to metal oxides because of oxidation of the metal at the surface of the molten metal bath or pool, both especially in the charge well of the furnace; excessive environmental pollution problems due to combustion of vaporizable and flammable chip contaminants such as oil, lacquer, or the like, at the surface of the molten metal bath in the charge well; and the necessity of employing thermal and/or chemical steps for burning off of such vaporizable and flammable contaminants from the chips, as in a rotary-drum type combustion apparatus, to eliminate such contaminants to as great an extent as possible before introduction of the chips into the molten metal bath so as to eliminate excessive flaming and combustion of such vaporized impurities at the surface of the molten metal bath, especially in the charge well, with its attendant difficulty of removal of products of combustion and concurrent pollution of the environment from such undesirable byproducts of the procedure.
Although it is still necessary to dry the metal chips, as by the employment of a chip wringer, ordinarily in combination with a heated cyclone separator or rotary dryer, such as the type manufactured by Premelt and sold under such trademark, to provide essentially dry metal chips, because such "dryness" is essential to avoid highly undesirable and even explosive reactions involving dissociation of water carried thereon and spontaneous combustion of the evolved hydrogen gas, before introduction of the chips into the charge well of a reverberatory furnace, or into a channel-type induction furnace or a coreless-type induction furnace, usually after separation of the chips of a nonferrous type from ferrous or other magnetic-type chips, the previous practice of chemically and/or thermally burning off vaporizable and flammable impurities such as oil, grease, lacquer, and the like has added serious economic disadvantages and impediments to the fullest utilization and re-utilization of metal chips by conversion into industrially-utilizable metal, especially "new" metal as obtained by recycling of metal chips from the fragmentation of previously-used commercial forms of the metal, such as aluminum or aluminum alloy cans or other used beverage container or the like.
Also, although recent developments in the art have permitted substantial improvements by way of introduction of the metal chips, and especially scrap metal chips, into the molten metal pool at or below the surface thereof by means of a chip-charging device of the nature of a compacting briquetter or a compacting extruder, no effective method or means for elimination of the foregoing shortcomings of the prior art have heretofore been available, despite a long-standing need for the same in order to facilitate and render more economic the conversion of such metal chips into industrially-utilizable metal which can be employed for all of the usual purposes and in all of the usual forming equipment, such as extruders, dies, and the like, where metal chips themselves are of course of no utility whatever.
The method and apparatus of the present invention provide long-awaited improvements in both the process and the apparatus for the utilization of metal chips involving the necessary step of introducing the same into a molten metal bath at the commencement of their re-entry into the stream of commerce, essentially by the maintenance of a non-oxidizing atmosphere at the surface of the molten metal bath or pool in the furnace charge well and the employment of appropriate charge-well cover means for the retention of inert or vaporized gases at the surface of the molten metal pool or mass and, advantageously, appropriate associated hood means for the removal of the products of combustion of the vaporizable and flammable gases, which do escape from the charge well, from the immediate vicinity and to a removed location where they can more conveniently be eliminated with minimization of environmental contamination.